What are the possible reasons one cannot accept an offer on Upwork?
The pop-up message show "ask client to withdraw the offer and make another one" whereas, you are now unable to reach the client
I havent come across that message before but usually if you cannot reach the client or the job post has been deleted - it means that the job post was marked as spam and was removed.
What do you mean by 'cant reach the client' - is the client offline or are the messages deleted?
If the messages are deleted, it might also mean that the client was removed for ToS violation